Wireless local area networks, for instance, IEEE 802.11, have been increasingly used for streaming multimedia in the home. With the increased home-use of real-time, or live, video-rich content, and high-definition (HD) television, more content is transmitted over wireless endpoints delivered over 802.11 links.
Transmitting HD video over IEEE 802.11 poses unique challenges due to the error-prone underlying physical layer (PHY), which may result in unpredictable chunks of packet losses. Congestion may exacerbate these problems and lead to further losses. The challenges are aggravated for HD video which has a large number of packets per video frame.
The IEEE 802.11a/b/g/n distributed coordination function and PHY provide methodologies and mechanisms to adapt to these losses. These mechanisms include collision detection, retransmission back-off counters and limits, and various modulation and coding rates. All of these impact achievable bit-rate and latency. In addition, the 802.11e specification addresses quality of service (QOS) for multimedia and provides access classes designed to provide better throughput and network access for voice and video streams.
To further improve media streaming over 802.11, a number of cross-layer design strategies have been proposed that share information and provide control across boundaries that are normally kept separate by network protocol and operating system application programming interface layering. Some proposed cross-layer strategies generally require either a significant modification of existing wireless systems, or provide some unreliable error recovery mechanisms such as forward error correction codes.
Some adaptation strategies include support of server adaptation by addition of application-level client feedback. Client feedback for video streaming may be performed using application-level protocols and may involve a specially designed matching client. Unfortunately, client feedback requires additional wireless bandwidth for sending the status reports and incurs significantly greater latency. Further, some application-level methods for estimating available instantaneous bandwidth send special probing data that does not benefit the video stream and consumes bandwidth. These strategies are most relevant when the limiting link in the network is either unknown or uncontrollable and directly observable.